1. Field of the Invention
The present invention relates to the field of hydraulic valve actuation adapted for internal combustion engines.
2. Prior Art
At the present time, piston-type internal combustion engines of interest to the present invention are currently widely used in automobiles, trucks, buses and various other mobile and stationary power systems. Such engines include the common gasoline and diesel engines, as well as similar engines operating from alternative fuels such as liquid propane. These engines commonly utilize intake and exhaust valves that are spring loaded to the closed position and which are directly or indirectly opened at appropriate times by a camshaft mechanically driven from the engine crankshaft. In a four-stroke engine, the camshaft is driven through a two-to-one reduction drive system (gear or chain or belt, etc.) to rotate at one-half the engine crankshaft speed.
Camshaft actuation of engine valves historically has had a number of advantages, resulting in its relatively universal use in such engines for many decades. These advantages include high reliability, particularly given the current level of development of such cam actuated valve systems. Cam actuation is also relatively cost effective, again given the state of development and quantities in which it is produced. Cam actuation also has the advantage of allowing shaping the cam to provide a smooth curve defining intake or exhaust valve position versus camshaft angle. This results in a rather low velocity takeoff and initial valve opening, as well as a rather low velocity valve final closing at low engine speeds, resulting in minimum noise being generated. It also results in faster valve opening and valve closing at higher engine speeds as required to maintain the same valve timing throughout the engine speed operating range.
Engine valve systems are facing more and more challenges that are becoming of increasing concern. In particular, optimal valve timing and lift are not fixed throughout the engine operating range. For instance, optimal valve timing and lift for maximum power at one engine speed will not be the same as optimal valve timing and lift for maximum power at another engine speed. Accordingly, the classic cam operated valve systems utilize a compromised valve timing and lift, providing compromised performance over a certain range of engine operating conditions while being less than optimal for most, if not at all, these conditions. Further, valve timing and lift for maximum power at any engine speed may not be optimal from an engine emissions standpoint. Optimum valve timing and lift at any given engine speed may need to be dependent on other dynamic engine parameters, such as one or more of engine loading, air temperature, air pressure, engine temperature, etc.
Recently, mechanisms have been introduced to attempt to make up for some of the limitations in the fixed timing and lift cam operated valve systems. These mechanisms include mechanisms for somewhat varying valve timing with engine speed, as well as mechanisms for also increasing the valve open duration. However, such mechanisms-tend to be complicated, open the valve a fixed distance under all engine operating speeds and are limited in the number and range of variables for which valve operation may begin to be optimized.
Recently, various hydraulic systems for valve actuation have been proposed. These systems offer the potential of more flexible control of valve actuation parameters over the range of the various engine operating parameters. The present invention is an improvement on these systems.
Hydraulic engine valve actuation systems and methods for internal combustion engines are disclosed herein. The systems utilize a proportional valve to regulate the flow of a working fluid to and from a hydraulic actuator controlling the engine valve position. The position of the proportional valve is controlled by high speed valves to control various engine valve parameters, such as one or more of engine valve takeoff and landing velocities, opening and closing velocities, valve lift, and/or valve timing and/or duration. Consistently, returning all valves to a known reference or starting position between engine valve events avoids accumulation of errors in proportional valve positioning. Exemplary embodiments using spool or poppet valves for the high speed pilot valves and a spool valve for the proportional valve, and spring return and/or hydraulic return for the engine valve, are disclosed.
To provide enhanced control over the engine valve operation, a specially shaped spool in the proportional valve may be used to control the flow area versus spool position. This allows more gradual restricting of the flow area versus spool movement over selected portions of the possible spool positions, diminishing the effect of small errors in spool position in such regions without inhibiting the maximum flow areas when the spool is at its maximum working fluid delivery positions.
Various further alternate embodiments are disclosed.